Silkworm cocoon material is a natural composite consisting of silk fi
bres and sericin glues. Both domestic and wild silkworms produce cocoons
but with different functionality – one selected
by man for textile manufacture whereas the other selected
by Nature to provide damage-tolerant housing. To understand the structure-–property relationship of cocoons, we evaluated and compared the
microstructure and mechanical properties of two representative cocoon walls. It appears that a “
brittle and weak” composite is produced
by domestic
Bombyx mori (
B. mori) while a “tough and strong” composite is made
by wild
Antheraea pernyi (
A. pernyi). The superior mechanical performance of
A. pernyi cocoons can
be attri
buted to
both the material properties and the fi
bre network
microstructures. Failure mechanisms and different failure modes for cocoon fi
bre composites were also proposed. A finite element model revealed qualitatively the effect of fi
bre properties and inter-fi
bre
bonding strength on the mechanical properties of the fi
bre network. It emerged that
both good mechanical properties of fi
bres and ro
bust inter-fi
bre
bonding were required for tough and strong fi
bre composites. The new insights could inspire new designs of synthetic fi
bre composites with enhanced mechanical properties.
bsSec_2">Statement of Significance
Natural cocoons are an important group of natural fibre composites with versatile functionalities. Previous studies have focused on the diversity of cocoon species and different morphological and mechanical features. It was suggested that the cocoon network structure determined the final mechanical properties of the cocoon composite. Nevertheless, the full structure–propertyfunction relationships for the cocoon composite are not understood. By studying two distinct cocoon species with specific functionalities, we prove that the mechanical properties of two cocoons are determined by both network properties and fibre properties. A robust fibre network is the prerequisite, within which the good mechanical properties of the fibres can play a part. The finding will inspire new designs of synthetic composites with desirable and predictable mechanical properties.